Neutron irradiation of (MgB2)-B-11: From the enhancement to the suppression of superconducting properties

In this letter, we present the effect of neutron irradiation up to fluences of 1.4x10(20) cm(-2) on the superconducting properties of MgB2. In order to obtain a homogeneously distributed disorder, the experiment was carried out on bulk samples prepared with the B-11 isotope. Up to fluences of 10(18) cm(-2), the critical temperature (T-c) is slightly diminished (36 K) and the superconducting properties are significantly improved; the upper critical field is increased from 13.5 T to 20.3 T at 12 K and the irreversibility field is doubled at 5 K. For the largest neutron fluence, T-c is suppressed down to 9.2 K and the superconducting properties come out strongly degraded.